Thrallherd is THE psionic PrC. It's like Incantatrix for a Wizard or Planar Shepherd for a Druid, though not automatically broken good.
If optimized, I'd argue it is actually more powerful than either of those, though, because you can have
those guys as your
thralls.
And if you get bored with them, you can kill them off, and get someone to replace them the next day with no penalty!
I think Thrallherd is arguably the most powerful PrC in the entire game if optimized well, just because it is Leadership Squared, and Leadership is hands down the most powerful feat in the game.